Mechanism and quantification of melt pool morphology evolution in single-track fabrication by laser directed energy deposition

By enabling the fabrication of complex, customized geometries, laser directed energy deposition (LDED) has emerged as a powerful technique for producing thin-wall structures widely employed in the aerospace sector. Achieving high-dimensional accuracy and geometric uniformity in these structures relies on optimizing the quality of single-layer melt tracks, which is governed by the evolution of the melt pool during deposition. Key processing parameters, including laser power ( P ), scan speed ( v ), and powder feeding rate ( f ), directly affect the static geometry and dynamic fluctuations of the melt pool. In this study, we develop a computational fluid dynamics-based simulation to investigate the longitudinal evolution of melt pool morphology during the formation of SS316L single tracks, focusing on laser activation, steady-state, and deactivation stages. The melt pool expands and tilts during laser activation due to thermal imbalance, exhibits surface fluctuations in a flat → bulge → wave pattern during the steady state, and contracts centripetally as solidification progresses during deactivation. An in situ high-speed infrared imaging system is integrated into the LDED setup for real-time monitoring of the melt pool. High-throughput experiments spanning 360 P - v - f combinations are conducted and automatically analyzed to quantify static features and dynamic fluctuations of the melt pool. Based on these results, a quality metric for melt tracks is proposed to identify optimal processing windows, which are experimentally verified through the fabrication of thin-wall samples with improved dimensional fidelity and geometric uniformity. The findings of this work provide critical insights into melt pool dynamics and offer a systematic approach for the optimization of processing parameters in LDED.